Heat removal system for nuclear fuel assemblies

ABSTRACT

A system to remove heat from nuclear fuel assemblies is disclosed. Such heat removal system includes one or more units having a base and one or more plates extending outwardly therefrom, the units being adapted to fit in a nuclear fuel assembly when it is placed in a shipping cask. The plates of the heat removal device, which are formed of a heat conductive material, fit between the pins of the nuclear fuel assembly and convey heat from the assembly to the shipping cask, from whence it is removed to the atmosphere by conduction through the cask.

United States Patent 51 June6,1972

[54] HEAT REMOVAL SYSTEM FOR NUCLEAR FUEL ASSEMBLIES [72] Inventor:Robert W. Kupp, 227 Beechwood Road, Ridgewood, NJ. 07450 [22] Filed:Sept. 3, 1968 [21] Appl.No.: 756,882

[52] US. Cl. ..l65/47, 165/185, 250/106 R [51] Int. Cl ..F28i 7/00, G2 1h 5/00 [58] Field ofSearch ..l65/l62, 185, 186,47,D1G. 5; 250/106 R,108, 106 S; 62/3 [56] References Cited UNITED STATES PATENTS 2,965,81912/1960 Rosenbaum ..l65/DIG. 5 2,993,080 7/ 1961 Poganski 3,119,9331/1964 Allen ..250/106S 3,220,471 11/1965 Coe ..l65/D1G. 5 3,312,2774/1967 Chitouras et a]... 165/185 3,229,096 1/1966 Bonilla et al..250/l06 X Primary Elxaminer-William F. ODea Assistant Examiner-P. D.Ferguson Attorney-Brumbaugh, Graves, Donohue & Raymond ABSTRACT A systemto remove heat from nuclear fuel assemblies is disclosed. Such heatremoval system includes one or more units having a base and one or moreplates extending outwardly therefrom, the units being adapted to fit ina nuclear fuel assembly when it is placed in a shipping cask. The platesof the heat removal device, which are formed of a heat conductivematerial, fit between the pins of the nuclear fuel assembly and conveyheat from the assembly to the shipping cask, from whence it is removedto the atmosphere by conduction through the cask.

6 Claim, 5 Drawing Figures PATENTEDJUH s 1972 3, 667. 540

sum 2 [IF 2 his ATTORNEYS HEAT REMOVAL SYSTEM FOR NUCLEAR FUELASSEMBLIIE This invention relates to a heat removal system for nuclearfuel assemblies when in shipping containers or casks.

Nuclear fuel assemblies must be taken to reactors for use or fromreactors for renovation or destruction after a predetermined timeinterval. Transportation of the nuclear fuel assemblieshas presentedmany difficulties due to their generation of heat during transportation,sometimes over extended distances requiring long periods of time. Sincethe fuel assemblies are highly radioactive, large, heavy shielded casksare ordinarily used for shipping, and heat from the fuel cells must beremoved during the shipping process. It is the usual practice tocirculate liquid coolant through the casks to cool the fuel assemblies,but this arrangement may require pumps, heat exchangers and other unitsexternal to the casks. Consequently,.occurrencesmay happen whichinterfere with circulation of such coolant through the casks, or loss ofsuch coolant, for example, a capsized truck or derailed train or failureof any part of the system. Loss of coolant would result in an increasein temperatures within the fuel cells to a level sufiicient to cause thefuel assembly pins to rupture and release hazardous fission products.For example, the heat generated within a typical fuel assembly withoutcoolant fairly rapidly increases the interior temperatures of the fuelassembly to a level on the order of 1000 to 1500 F., temperaturessufficient to cause failure of the fuel assembly (but not through anuclear explosion).

The present invention overcomes the aforementioned problems by providinga heat removal system that may be used alone or in combination withother cooling apparatus to prevent temperatures within the fuelassemblies from rising to dangerous levels while being transported. Moreparticularly, the system includes one or more units made of a heatconductive material which can be inserted into a fuel assembly inside ashipping cask to absorb and convey the heat from the central regions ofthe fuel assembly to its perimeter where the heat can be transferreddirectly or indirectly to the shipping cask and eventually to theatmosphere.

Although the invention may be used together with known cooling systemsas a failsafe system, in the event of a loss of coolant or coolantcirculation in the shipping cask due to an accident or failure of theprimary cooling system, it can also be employed independently in certainfuel assemblies to remove heat including the residual after-heatgenerated by fuel cells during shipping after use in a reactor.

The above and other advantages of the present invention will be morefully understood when the following description is considered inconnection with the accompanying illustrative drawings, in which:

FIG. 1 is a cross-sectional view in perspective of reactor nuclear fuelassemblies in a shipping cask in which the inventive cooling system hasbeen installed;

FIG. 2 is a perspective view of a typical inventive heat removal unit;

FIG. 3 is a partial cross-sectional view of a nuclear fuel assembly in ashipping cask in which an inventive heat removal system has beeninstalled;

FIG. 4 is a cross-sectional view of a nuclear fuel assembly having theinventive heat removal system of a different geometric shape designed tofit and cool the illustrated nuclear fuel assembly; and

FIG. 5 is a cross-sectional view of a shipping cask in which heatremoval units have been installed with their bases abutting each otherin the interior portion of the cask.

Referring to the drawings in detail, fuel assemblies 5 are placed in asuitably dimensioned shipping container or cask 6 having inner and outersteel walls 6a and 6b between which is sandwiched lead shielding 6c. Theheat removal system includes a plurality of units 7, as shown in FIGS. 1and 3. For clarity, the cask 6 is shown broken away and without top andend walls, but it will be understood that the fuel assemblies 5 aregenerally enclosed and sealed within the cask.

7 heat is conveyed by the plates 9 from the central regions 1 1 of a.

Referring to the units 7 in greater detail with particular reference toFIG. 2, each unit is formed of a heat conductive material, e.g., copperor aluminum, and in this embodiment resembles a comb with a base 8 andplates 9 extending therefrom. In the comb 7 shown in FIG. 2, the plates9 are of equal length, but they can be of varying length, depending onthe size and configuration of the nuclear fuel assembly within theshipping cask and the cooling requirements. For example, in FIG. 4 afuel assembly 5 and heat removal combs 7 have plates 9 of unequallength.

The plates 9 of the comb 7 fit between the rows of parallel heatgenerating pins 10 in the nuclear fuel assembly 5. Thus, a pin 10 in aninterior area 11 of the nuclear fuel assembly 5 radiates or has heatconducted to the plates 9 of the comb 7 adjacent to or contacting it.Similarly, the other pins 10 in a given row radiate or conduct heat tothe same plate 9, and the the nuclear fuel assembly to its perimeter.Note that physical contacts between the pins 10 and the plates 9 are notrequired although such contacts are advantageous and may be provided forwhen required.

In FIG. 1 the plates 9 of the heat removal comb 7 are of equal lengthbut only extend one-half way through the nuclear fuel assembly 5, andanother similar comb 7 is provided on the opposite side of suchassembly. In FIG. 3, the plates 9 of the combs 7 again are of equallength, but extend the complete distance through the nuclear fuelassemblies 5 because of the difierent arrangement of assemblies withinthe shipping cask. FIG. 4 shows a typical adaptation where the plates 9of the comb 7 are of unequal length to cool one large nuclear fuelassembly 5' within a shipping cask (not shown) requiring four separateheat removal combs.

The most effective and efficient way for the inventive cooling system toabsorb and convey the heat, including residual after-heat, from fuelcells, is for the comb 7 to be seated flush against the inside wall ofthe shipping cask 6, as shown in FIGS. 1 and 3, so that the heat istransferred by contact conduction from the comb 7 to the outer wall 6bof the shipping cask 6 and then by air convection and radiation to theatmosphere. However, if the heat removal combs do not contact to theshipping cask but are merely inserted between the nuclear fuel assemblyand the inside wall of the shipping cask, natural forces will cause theheat removal combs on the top and the sides of the nuclear fuel assemblyto be out of contact with the shipping cask. In these cases, thetransfer of heat from the comb is by liquid or gas convection andconduction as well as by radiation to the shipping cask walls. Moreover,as shown in FIG. 5, the bases 8 of the units 7 may abut each other ininterior portions of the cask 6, and then conduct the heat through thebases or through separators (not shown) in the cask to its exteriorwalls. For example, a separator could extend between the vertical wallsacross the upper units 7 located in the cask 6 of FIG. 1.

In typical fuel cells, the temperature drop between one of the pins 10,in the central area 11, and the end of one of the plates 9, isrelatively low, e.g., F., but the value depends upon fuel assemblyhistories and characteristics. Other pins 10 in a given line radiate orconduct heat to the same plate 9 and a typical temperature drop betweenthe free end of the plate and the base end of the plate is on the orderof 25 F.

While the invention has been particularly described as applied tonuclear fuel assemblies as shown in FIGS. 1 and 3, it will be readilyunderstood that the novel heat removal system may be readily adapted foruse with a variety of differently configured nuclear fuel assemblies invarious shipping casks. For example, it may be desirable in certainnuclear fuel assemblies to provide cooling units each comprised of abase 8 with only a single plate 9 extending outwardly therefrom.Therefore, the invention is not intended to be limited to the specificapparatus disclosed herein but is to be defined by the appended claims.

I claim:

l. A heat removal system for a nuclear fuel assembly comprising acontainer including an inside perimeter, a fuel assembly including atleast one row of a plurality of substantially parallel fuel pin elementspositioned within the container, a cooling unit including a basepositioned in close proximity but not fastened to the inside perimeterof the container and further including at least one plate extending fromthe base to a position between the fuel pin elements, whereby heat fromthe fuel pin elements in proximity to the plate is absorbed by the plateand conveyed to the base, the base and plate being formed of a heatconductive material.

2. A system as defined in claim 1, wherein the plates extending from thebase are equal in length.

3. A system as defined in claim 1, wherein the plates extending from thebase are graduated in length, and at least four units are inserted intothe fuel assembly from different directions.

4. A system as defined in claim 1, wherein the plates extend to aboutthe middle of the fuel assembly.

5. A system as defined in claim 1, wherein the plates extendsubstantially through the fuel assembly.

6. A heat removal system for a nuclear fuel assembly, comprising acontainer having walls with inner faces that define the interior portionof the container, a fuel assembly having at least one row of a pluralityof substantially parallel fuel pin elements positioned within theinterior portion of the container, a cooling unit having a base with atleast one plate extending therefrom to a position between the fuel pinelements, the base of the cooling unit being positioned in the interiorportion of the container remote from at least one of the inner faces,and a portion of the base of the cooling unit being positioned in closeproximity to another of the inner faces so that heat from the fuel pinelements in close proximity to the plate is absorbed by the plate andconveyed therethrough and through the base to the base portion that isin close proximity to the other inner face.

1. A heat removal system for a nuclear fuel assembly comprising acontainer including an inside perimeter, a fuel assembly including atleast one row of a plurality of substantially parallel fuel pin elementspositioned within the container, a cooling unit including a basepositioned in close proximity but not fastened to the inside perimeterof the container and further including at least one plate extending fromthe base to a position between the fuel pin elements, whereby heat fromthe fuel pin elements in proximity to the plate is absorbed by the plateand conveyed to the base, the base and plate being formed of a heatconductive material.
 2. A system as defined in claim 1, wherein theplates extending from the base are equal in length.
 3. A system asdefined in claim 1, wherein the plates extending from the base aregraduated in length, and at least four units are inserted into the fuelassembly from different directions.
 4. A system as defined in claim 1,wherein the plates extend to about the middle of the fuel assembly.
 5. Asystem as defined in claim 1, wherein the plates extend substantiallythrough the fuel assembly.
 6. A heat removal system for a nuclear fuelassembly, comprising a container having walls with inner faces thatdefine the interior portion of the container, a fuel assembly having atleast one row of a plurality of substantially parallel fuel pin elementspositioned within the interior portion of the container, a cooling unithaving a base with at least one plate extending therefrom to a positionbetween the fuel pin elements, the base of the cooling unit beingpositioned in the interior portion of the container remote from at leastone of the inner faces, and a portion of the base of the cooling unitbeing positioned in close proximity to another of the inner faces sothat heat from the fuel pin elements in close proximity to the plate isabsorbed by the plate and conveyed therethrough and through the base tothe base portion that is in close proximity to the other inner face.